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Results of the Experiments
Results of the Experiments
7.10
The aluminium replaces the copper.
Initially the aluminium is not very
reactive (it has an oxide coating on it) and
reaction takes place at the cut edges.
Brown copper is clearly seen along the
edges of the aluminium foil. Eventually
most of the aluminium reacts and it
disintegrates. Aluminium sulphate is
formed. The word equation for the reaction
is: alu copper sulphate
aluminium sulphate.
7.11
The word equation for the reaction is: zinc
+ copper sulphate zinc
sulphate. You can add a little acid to the
zinc carbonate, it will fizz as carbon
dioxide is produced.
7.12
Yes magnesium does replace iron.
The word equation for the reaction is:
mag iron sulphate iron
+ magnesium sulphate.
7.13
Aluminium replaces iron, but not as readily
as does magnesium. The word equation
for the reaction is: alu iron
sulphate iron + aluminium
sulphate. Magnesium is the most reactive
and copper the least reactive metal.
8.1
Copper reacts with oxygen in the air
to give black copper oxide. Inside the
envelope the copper is still bright and
shiny. It has got hot but oxygen cannot
get to it to form copper oxide.
8.2
Iron reacts to give black iron oxide.
8.3
The iron filings burn to iron oxide.
They are so small that they burst into
flame and sparkle as they fall through the
burner flame. “Sparkler” fireworks contain
iron filings.
8.4
It does not obviously oxidise, but if the
aluminium foil is thin enough it melts.
8.5
Magnesium burns to give white
magnesium oxide ash.
8.6
The copper carbonate darkens as it
decomposes giving off carbon dioxide gas
and leaving black copper oxide on the
evaporating spoon. You could dissolve the
copper oxide in acid to give a blue copper
salt.
8.7
Tartaric acid melts, the liquid boils, there is
a little vapour and virtually no black carbon
residue in the evaporating spoon.
8.8
Citric acid melts and boils. There is a lot
of white smoke that catches fire. The small
amount of black carbon residue is light
and fluffy.
8.9
The ammonium chloride disappears from
the bottom of the test tube and condenses
on the cool upper part of the test tube.
9.1
The lime water turns milky showing that
you are blowing carbon dioxide gas
through it.
9.2
The lime water slowly turns milky showing
that air contains carbon dioxide gas.
9.3
The universal indicator goes yellow
showing that carbon dioxide is a weak
acid in solution. 9.4 Universal indicator
solution is yellow showing that sparkling
water is a weak acid.
9.5
The lime water rapidly turns milky showing
that carbon dioxide gas is being expelled
from the sparkling water.
In Experiment 9.4 the indicator is put into
the solution. In this experiment the carbon
dioxide gas is boiled out. Other acids that
might have been added to the fizzy soft
drink do not boil out of the solution, and so
do not spoil this experiment.
9.6
The lime water goes milky showing
that carbon dioxide is produced in the
flame. The black deposit is carbon.
Tiny carbon particles, called soot, are
produced in many flames where air or
oxygen is not mixed with the other fuel.
A candle, for example, burns with a
similar sooty flame.
9.7
The lime water rapidly turns milky showing
that carbon dioxide gas is produced.
9.10
The indicator is blue-violet. Ammonia
is a strong alkali.
9.12
The oxygen in air turns the green iron(II)
hydroxide into brown iron(III) hydroxide as
in Experiment 7.4.
9.13
Aluminium hydroxide is a white precipitate.
9.14
The oxygen has reacted with the iron
filings to form iron oxide.
About 1/5 of the test tube fills with water.
This has replaced the oxygen so air is
about 1/5 oxygen. The main gas left is
nitrogen. The iron filings have gone
black-brown as they rust.
9.15
The nail in the dry tube remains bright and
shiny. The nail in the boiled water will also
be bright and shiny if all the air has been
removed from the water. The two nails in
the crystallising dishes will be rusting.
That with sodium chloride should show
more rust than that in water only. For iron
to rust both water and oxygen are
necessary. Rust is an iron hydroxide.
The word equation for the reaction is:
iron + water hydrated
iron oxide (rust).
9.17
The glowing splint readily reignites
in the oxygen gas. The iron sulphate helps
the hydrogen peroxide to decompose into
oxygen and water. It is a catalyst. The clay
pot is there to provide sharp points on
which the oxygen bubbles can form so
they come smoothly out of the solution.
9.18
The green solution goes brown. The colour
changes are the same as in Experiment
9.12. In both experiments green iron(II)
is being converted into brown iron(III).
9.19
Yes the blue colour disappears.
9.20
The cut apple quickly browns in air (some
varieties of apple quicker than others).
That with vitamin C on it does not go
brown. The oxidation by the oxygen
in air is stopped by the vitamin C.
10.5
Lemon juice and orange juice both contain
vitamin C, and decolourise the test
solution.
11.1
The sugar melts and boils and burns
leaving a large amount of carbon residue
in the evaporating spoon. Tartaric and
citric acids leave much less carbon
residue.
11.5
The orange copper oxide formed from the
copper sulphate in the Fehling’s solution
is different from the black copper oxide
supplied. The black oxide is copper(II)
oxide. The orange oxide is copper(I) oxide.
